Two-speed winding for three-phase motors.



No. 785,533. PATENTED MAR. 2l, 1905.

* E. F. W. ALEXANDERSON. TWO SPEED WINDING FOR THREE PHASE MOTORS.

APPLICATION FILED AUG.13, 1904.

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Patented March 21, 1905.

UNITED STATES PATENT OEEICE.

ERNST F. NV. ALEXANDFRSON. OF SCHFJNFCTA'DY, NEr YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF N ElY YORK.

TWO-SPEED WINOING FOR THREE-PHASE MOTORS.

SPECIFICATION forming part of Letters Patent No. 785,533, dated lfarch 21, 1905.

Application filed August 13, 1904. Serial No. 220,608.

To @ZZ 1.1171111111/ 'iff/ 711/1111/ concern:

Be it known that l, ERNST F. lV. ALEXAN- DEusoN, a subject of the vKing ot' Sweden and Norway, residing' at Schenectady, county ot Schenectady, State oi: New York, have invented certain new and useful Improvements in Two-Speed Tindings for lhree-lhase Motors, oit' which the following is a specification.

My invention relates to drum-windings for three-phase motors; and its object is to reduce the number of slots required for a variablespeed three-phase motor with certain speed ratios. In drum-windings as ordinarily arranged in order to produce evenlyspaced poles, while at the same time permitting the use ot' former-wound coils, a total number oi' slots is chosen which is a multiple of the number oi poles and the number of phases. lVith a three-phase winding 'For a large number of poles the above arrangement necessitates a large number of slots. Furthermore, when it is attempted to design such a winding Yfor more than one number of poles the total number of slots must be a multiple not only of the number ot' phases, but also oi both numbers of poles. l/Vith high-potential machines the cost and difliculty of insulating` the armaturecoils increase with the number of slots, so that a variable-speed three-phase winding for high potentials and a large number of poles becomes excessively expensive.

The object of my invention is to provide a novel winding for three-phase machines which will give certain ratios ot' pole-numbers, so as to produce a variable-speed motor with a minimum number oi' slots.

My invention consists in providing the motor with two windings, one of the ordinary three-phase type and the other a two-phase winding' connected for three-phase operation. As has been said, the total number ot' slots must be a multiple of the number or' poles and number of phases. Consequently it follows that for a given number of poles the minimum number oi' slotsrequired for a two-phase winding is only two-thirds of the number required 'for a three-phase winding, or, stated another way, with a given number of slots ifty per cent. more poles may be produced with a two-phase winding than with a threephase winding.

My invention will best be understood by reference to the accompanying' drawings, in whichA Figure l shows diagrammatically the windings otl a machine arranged in three-phase and two-phase in accordance with my invention. Fig. 2 shows a development ot' the two windings.

Although in the drawings the two windings are shown separately for the sake oT clearness, it will be understood that they are to be placed in the same slots. This is indicated in Fig. Q by the dotted lines extending across the two sets o'tl conductors, which are shown one immediately below the other.

In the drawings, A R C represent the three phases of an ordinary three-phase winding, which in this easel have shown as Y-connected.

D and E represent the two phases ot' a twophase winding connected in T in the manner well known in the art to adapt it for threephase operation.

S represents a switch by means of which either oi the two windings may be connected to a source ot' current 'l 2 3. The switch-terminals are indicated by small letters corresponding to the several phases -of the motorwinding to which they are connected.

The development of the two windings is clearly shown in Fig. 2. For the sake otl clearness only the phase A of the three-phase winding is shown in full lines, the other two phasesbcing shown in dotted lines. The arrow-heads indicate the relative distribution o'l" current at any moment. Current is supposed to be entering phase A at terminal L and dividing upon reaching the neutral point and passing out through the phases B and C in parallel. lt will be seen that eight poles are produced by the winding, which is contained in twenty-four slots, this number being the least common multiple ot the number ot' poles and number of phases. The lower portion ol Fig. 2 shows a development ot' the two-phase winding. The arrows show the relative directions ot' the currents in the conductors at any given moment when this winding is connected to the source. The current is supposed to be entering at terminal Z of phase D and on reaching the point of connection ot' windings D and E dividing and passing out through the other portion of phase D and phase E in parallel. An inspection of the arrows shows that twelve poles are produced, the total number of slots again being the product ot' the number of poles and the number of phases. Thus by means of the separate windings-one three-phase and the other two phase-I am enabled to obtain either eight or twelve poles with twenty-four slots, whileif an ordinary three-phase winding were used seventy-two slots would be required for the same polar ratios.

Although I have shown the windings arranged to produce merely the speed ratio of two to three, it is evident that certain other ratios involving a multiple of one of these numbers may be obtained, the essential thing being that the two windings may occupy the same number of slots. Thus if the two-phase winding shown in the drawings is given twice the pitch shown without any other change it would producesix poles instead of twelve, giving a speed ratio of four to three instead of two to three, and would still fit into the slots of the three-phase winding.

Consequently I do not desire to limit myself to the particular arrangement herein shown; but I aim in the appendedl claims to cover all modilications which are within the scope of my invention.

I/Vhat I claim as new, and desire to secure vby Letters Patent of the United States, is

1. In an alternating-current motor, a threephase winding, a two-phase winding in the same slots therewith, and means for connecting either winding to a source of three-phase current.

2. In an alternating-current motor, a threephase winding, a two-phase winding ol" ditlerent pitch in the same slots therewith, and means for connecting either winding to a source of current.

3. In an alternating-current motor, a threephase winding, a two-phase winding of a diiierent number of poles in the same slots therewith, and means for connectingeither winding to a source of three-phase current.

4. In an alternatiiig-current motor, a threephase winding', and a T-connected two-phase winding in the same slots therewith.

In witness whereoil I have hereunto set my hand this 12th day of August, 1904.

l'llllS'l li. W. ALEXANDERSON. Witnesses:

BENJAMIN B. HULL, HELEN OHFoRD. 

